Variable transmission reticle for charged particle beam lithography tool
AssigneeNikon Corporation
InventorMichael S. Gordon
Life of this patent
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Abstract
A compound reticle having generally complementary clear and opaque areas on a portion of subfield in each of two reticle layers which can be moved relative to each other form a variable transmissivity shutter to regulate charged particle beam intensity independently of source beam current. Either homogeneous or inhomogeneous (e.g. having local variations in beam current density) can be produced at will and in rapid succession to study effects of beam current on beam pattern resolution and aberrations as well as optimum focus for particular patterned subfields having respectively differing transmissivities.
Claims15
A compound reticle for testing a charged particle beam projection system including
- a first reticle layer having patterned areas, opaque areas and clear areas thereon,
- a second reticle layer having opaque areas and clear areas thereon, said opaque areas and clear areas being substantially complementary to clear areas and opaque areas, respectively, on said first reticle layer, and
- means for moving one of said first reticle layer and said second reticle layer relative to the other of said first reticle layer and said second reticle layer.
A method for controlling beam current in a charged particle beam projection lithography tool including steps of
- illuminating a subfield of a compound reticle having two reticle layers with a beam of charged particles, a subfield of one of said two reticle layers having opaque, clear and patterned areas thereon and a subfield of another of said reticle layers having clear areas complementary to opaque and patterned areas and opaque areas complementary to clear areas on said one of said reticle layers, and
- moving one of said reticle layers relative to another of said reticle layers.
Dependencies are inferred from the claim text.